In previous studies we have gained considerable insight into the mechanisms by which adenylate cyclase is regulated by cations, hormones, guanine nucleotides, fluoride, and adenosine. We have found that adenosine inhibits adenylate cyclase non-competitively with respect to metal-ATP and in a cation dependent manner. Stimulated form(s) of the enzyme were potently inhibited whereas the basal enzyme was not. We intend to take advantage of these earlier observations: a) To identify sub-cellular fractions in addition to plasma membranes that may be enriched in adenylate cyclase(s) sensitive to stimulation by fluoride, guanine nucleotides, or glucagon, or sensitive to inhibition by adenosine. b) To identify and then purify by affinity chromatography a protein to which adenosine binds to exert its inhibitory effect on adenylate cyclase. c) To ascertain whether the effect of adenosine to lower cellular cAMP levels is due to inhibition of adenylate cyclase or to stimulation of cyclic nucleotide phosphodiesterase. D) To ascertain whether adenosine behaves cooperatively with insulin to enhance insulin's effects in isolated fat cells to decrease cAMP levels, to decrease lipolysis, and to increase glucose metabolism. e) To ascertain whether the effects of adenosine on fat cell metabolism and cAMP levels may be due to a direct action of adenosine or may be mediated by a factor generated in response to adenosine.